The present invention relates to a slot type extrusion die for the extrusion of thermoplastic sheet, film, strand, strip, etc. Such extrusion dies are presently known and generally include an entrance for the extrudate into the die itself, a manifold area for the distribution of the thermoplastic material within the die and an exit slot or slots whereby the ultimate shape of the material is determined as it emerges from the die. With such die constructions, it is generally necessary to equalize the pressure drop through the die so as to insure that an equal amount of material is delivered along the full width thereof. Such pressure equalization may be accomplished by the use of an adjustable restrictor bar generally extending laterally across the extent of the flow channel and movable into and out of the flow path thereof so as to form in effect an adjustable valve mechanism to create various differential pressure drops across the internal flow path of the die as needed to effect the desired shape of the material extruded. Generally dies of the above described construction include a plurality of elongated studs fixedly connected to the restrictor bar at spaced locations therealong. These studs are axially positioned through the die body and terminate in threaded outer ends which extend beyond the die body itself. Accordingly, various systems have been devised to rotationally engage the outer ends of the studs with some axially restrained member such as a nut and in this way cause the studs to axially move with respect to the die body and accordingly facilitate the required adjustment of the restrictor bar in turn connected thereto. Accordingly, progressive rotation of the nut devices about their respective studs in opposite directions effects the necessary forward and rearward movement to the restrictor bar necessary for the required material flow adjustment. However, with such systems, rotational overstressing of the stud via the nut device can cause the stud to break. Stud breakage is particularly undesirable if it occurs internally of the die, e.g. at its connection point with the restrictor bar since such breakage would require at least partial disassembly of the die and interruption of its production time. Accordingly, it would be desirable that any such stud breakge occur at a location outside of the die so that the broken end would be readily accessible and thus more easily removed without the necessity of shutting down the die. A construction designed for such purposes is disclosed in U.S. Pat. No. 3,859,032 issued Jan. 7, 1975, and includes a weakened stud portion at which any breakage would occur. Such construction and its operational systems, however, requires rotationally disconnecting the broken stud segments from the restrictor bar which in many cases is difficult to achieve. Accordingly, it would be further desirable to be able to operationally interrupt the application of rotational force to the stud at a point prior to which the stud itself is broken and thus simultaneously eliminate the cost associated with stud replacement and the often extensive labor factor in removing broken studs from the die body. The above art discussion and patent citation constitutes applicant's Prior Art Statement and a copy of the cited patent is thus enclosed with this application.
This and other objects of the present invention are accomplished by the use of a stud adjustment assembly including spools adapted for engagement with the threaded stud ends which extend outside of the die body. Each of the spools includes a threaded axial bore adapted for engagement with the stud and including means breakable upon rotational overstressing thereof so as to prevent further force application to its respective stud. In this manner, the fully accessible spools are replaced rather than the adjustment studs or other more time consuming element.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawing.